Why regular expression '[a-z][0-9]+$' not work
up vote
0
down vote
favorite
I use the regular expression to handle the string "abc123".
The command below is work and return value "c123"
echo abc123 | grep -o [a-z][0-9]*$
But the command below does not work.
echo abc123 | grep -o [a-z][0-9]+$
Why do I get this result?
I knew the '*' is used to matches the preceding pattern element zero or more time, and '+' is used to matches the preceding pattern element at least one or more time.
So this situation makes me confused.
regular-expression
edited 2 days ago
Rui F Ribeiro
38.5k1479128
asked 2 days ago
IsaraSu
31
New contributor
IsaraSu is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |
up vote
0
down vote
favorite
I use the regular expression to handle the string "abc123".
The command below is work and return value "c123"
echo abc123 | grep -o [a-z][0-9]*$
But the command below does not work.
echo abc123 | grep -o [a-z][0-9]+$
Why do I get this result?
I knew the '*' is used to matches the preceding pattern element zero or more time, and '+' is used to matches the preceding pattern element at least one or more time.
So this situation makes me confused.
regular-expression
edited 2 days ago
Rui F Ribeiro
38.5k1479128
asked 2 days ago
IsaraSu
31
New contributor
IsaraSu is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |
up vote
0
down vote
favorite
up vote
0
down vote
favorite
I use the regular expression to handle the string "abc123".
The command below is work and return value "c123"
echo abc123 | grep -o [a-z][0-9]*$
But the command below does not work.
echo abc123 | grep -o [a-z][0-9]+$
Why do I get this result?
I knew the '*' is used to matches the preceding pattern element zero or more time, and '+' is used to matches the preceding pattern element at least one or more time.
So this situation makes me confused.
regular-expression
edited 2 days ago
Rui F Ribeiro
38.5k1479128
asked 2 days ago
IsaraSu
31
New contributor
IsaraSu is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
I use the regular expression to handle the string "abc123".
The command below is work and return value "c123"
echo abc123 | grep -o [a-z][0-9]*$
But the command below does not work.
echo abc123 | grep -o [a-z][0-9]+$
Why do I get this result?
I knew the '*' is used to matches the preceding pattern element zero or more time, and '+' is used to matches the preceding pattern element at least one or more time.
So this situation makes me confused.
regular-expression
regular-expression
edited 2 days ago
Rui F Ribeiro
38.5k1479128
asked 2 days ago
IsaraSu
31
New contributor
IsaraSu is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 2 days ago
Rui F Ribeiro
38.5k1479128
asked 2 days ago
IsaraSu
31
New contributor
IsaraSu is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 2 days ago
Rui F Ribeiro
38.5k1479128
edited 2 days ago
Rui F Ribeiro
38.5k1479128
edited 2 days ago
Rui F Ribeiro
38.5k1479128
38.5k1479128
asked 2 days ago
IsaraSu
31
New contributor
IsaraSu is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 2 days ago
IsaraSu
31
asked 2 days ago
IsaraSu
31
31
New contributor
IsaraSu is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
IsaraSu is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
IsaraSu is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |
add a comment |
2 Answers
2
active
oldest
votes
up vote
4
down vote
accepted
+ is only a quantifier in extended regular expressions (ERE):
$ echo abc123 | grep -Eo '[a-z][0-9]+$'
c123
In basic regular expressions (BRE) it matches literal +, although you can use {1,} instead, or in GNU grep (-o is already a GNU extension anyway), +:
$ echo abc123 | grep -o '[a-z][0-9]+$'
c123
(note the quotes to prevent [ and from being interpreted by the shell).
edited yesterday
Stéphane Chazelas
297k54562907
answered 2 days ago
steeldriver
34.1k34983
Just a comment on @StéphaneChazelas' edit:-ois a GNU extension, but it's also available in (some) othergrepimplementations. However,+in a basic regular expression is GNU-only as far as I know.
– Kusalananda
yesterday
@Kusalananda, I agree it's a bit of a shortcut. Several other implementations have picked some of the GNU extensions over the years.+is also found in some non-GNU implementations like busybox or ast-open. Also note that many BSDs still use a fork of an old GNUgrep, so will support old GNU extensions like those.
– Stéphane Chazelas
yesterday
add a comment |
up vote
0
down vote
+ in grep need to be escaped to take effect. Instead of
echo abc123 | grep -o [a-z][0-9]+$
You need to write
echo abc123 | grep -o '[a-z][0-9]+$'
There are other characters that need to be escaped as well. It is also good practice to put your regex in single quotes.
You can also use egrep which is a synonym of grep -E and uses Extended RE, as commented by @muru.
answered 2 days ago
Weijun Zhou
1,468224
Or use ERE with-E
– muru
2 days ago
The escaped+in basic regular expressions is a non-standard GNU extension.
– Kusalananda
2 days ago
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
4
down vote
accepted
+ is only a quantifier in extended regular expressions (ERE):
$ echo abc123 | grep -Eo '[a-z][0-9]+$'
c123
In basic regular expressions (BRE) it matches literal +, although you can use {1,} instead, or in GNU grep (-o is already a GNU extension anyway), +:
$ echo abc123 | grep -o '[a-z][0-9]+$'
c123
(note the quotes to prevent [ and from being interpreted by the shell).
edited yesterday
Stéphane Chazelas
297k54562907
answered 2 days ago
steeldriver
34.1k34983
Just a comment on @StéphaneChazelas' edit:-ois a GNU extension, but it's also available in (some) othergrepimplementations. However,+in a basic regular expression is GNU-only as far as I know.
– Kusalananda
yesterday
@Kusalananda, I agree it's a bit of a shortcut. Several other implementations have picked some of the GNU extensions over the years.+is also found in some non-GNU implementations like busybox or ast-open. Also note that many BSDs still use a fork of an old GNUgrep, so will support old GNU extensions like those.
– Stéphane Chazelas
yesterday
add a comment |
up vote
4
down vote
accepted
+ is only a quantifier in extended regular expressions (ERE):
$ echo abc123 | grep -Eo '[a-z][0-9]+$'
c123
In basic regular expressions (BRE) it matches literal +, although you can use {1,} instead, or in GNU grep (-o is already a GNU extension anyway), +:
$ echo abc123 | grep -o '[a-z][0-9]+$'
c123
(note the quotes to prevent [ and from being interpreted by the shell).
edited yesterday
Stéphane Chazelas
297k54562907
answered 2 days ago
steeldriver
34.1k34983
Just a comment on @StéphaneChazelas' edit:-ois a GNU extension, but it's also available in (some) othergrepimplementations. However,+in a basic regular expression is GNU-only as far as I know.
– Kusalananda
yesterday
@Kusalananda, I agree it's a bit of a shortcut. Several other implementations have picked some of the GNU extensions over the years.+is also found in some non-GNU implementations like busybox or ast-open. Also note that many BSDs still use a fork of an old GNUgrep, so will support old GNU extensions like those.
– Stéphane Chazelas
yesterday
add a comment |
up vote
4
down vote
accepted
up vote
4
down vote
accepted
+ is only a quantifier in extended regular expressions (ERE):
$ echo abc123 | grep -Eo '[a-z][0-9]+$'
c123
In basic regular expressions (BRE) it matches literal +, although you can use {1,} instead, or in GNU grep (-o is already a GNU extension anyway), +:
$ echo abc123 | grep -o '[a-z][0-9]+$'
c123
(note the quotes to prevent [ and from being interpreted by the shell).
edited yesterday
Stéphane Chazelas
297k54562907
answered 2 days ago
steeldriver
34.1k34983
+ is only a quantifier in extended regular expressions (ERE):
$ echo abc123 | grep -Eo '[a-z][0-9]+$'
c123
In basic regular expressions (BRE) it matches literal +, although you can use {1,} instead, or in GNU grep (-o is already a GNU extension anyway), +:
$ echo abc123 | grep -o '[a-z][0-9]+$'
c123
(note the quotes to prevent [ and from being interpreted by the shell).
edited yesterday
Stéphane Chazelas
297k54562907
answered 2 days ago
steeldriver
34.1k34983
edited yesterday
Stéphane Chazelas
297k54562907
edited yesterday
Stéphane Chazelas
297k54562907
edited yesterday
Stéphane Chazelas
297k54562907
297k54562907
answered 2 days ago
steeldriver
34.1k34983
answered 2 days ago
steeldriver
34.1k34983
answered 2 days ago
steeldriver
34.1k34983
34.1k34983
Just a comment on @StéphaneChazelas' edit:-ois a GNU extension, but it's also available in (some) othergrepimplementations. However,+in a basic regular expression is GNU-only as far as I know.
– Kusalananda
yesterday
@Kusalananda, I agree it's a bit of a shortcut. Several other implementations have picked some of the GNU extensions over the years.+is also found in some non-GNU implementations like busybox or ast-open. Also note that many BSDs still use a fork of an old GNUgrep, so will support old GNU extensions like those.
– Stéphane Chazelas
yesterday
add a comment |
Just a comment on @StéphaneChazelas' edit:-ois a GNU extension, but it's also available in (some) othergrepimplementations. However,+in a basic regular expression is GNU-only as far as I know.
– Kusalananda
yesterday
@Kusalananda, I agree it's a bit of a shortcut. Several other implementations have picked some of the GNU extensions over the years.+is also found in some non-GNU implementations like busybox or ast-open. Also note that many BSDs still use a fork of an old GNUgrep, so will support old GNU extensions like those.
– Stéphane Chazelas
yesterday
Just a comment on @StéphaneChazelas' edit:
-o is a GNU extension, but it's also available in (some) other grep implementations. However, + in a basic regular expression is GNU-only as far as I know.– Kusalananda
yesterday
Just a comment on @StéphaneChazelas' edit:
-o is a GNU extension, but it's also available in (some) other grep implementations. However, + in a basic regular expression is GNU-only as far as I know.– Kusalananda
yesterday
@Kusalananda, I agree it's a bit of a shortcut. Several other implementations have picked some of the GNU extensions over the years.
+ is also found in some non-GNU implementations like busybox or ast-open. Also note that many BSDs still use a fork of an old GNU grep, so will support old GNU extensions like those.– Stéphane Chazelas
yesterday
@Kusalananda, I agree it's a bit of a shortcut. Several other implementations have picked some of the GNU extensions over the years.
+ is also found in some non-GNU implementations like busybox or ast-open. Also note that many BSDs still use a fork of an old GNU grep, so will support old GNU extensions like those.– Stéphane Chazelas
yesterday
add a comment |
up vote
0
down vote
+ in grep need to be escaped to take effect. Instead of
echo abc123 | grep -o [a-z][0-9]+$
You need to write
echo abc123 | grep -o '[a-z][0-9]+$'
There are other characters that need to be escaped as well. It is also good practice to put your regex in single quotes.
You can also use egrep which is a synonym of grep -E and uses Extended RE, as commented by @muru.
answered 2 days ago
Weijun Zhou
1,468224
Or use ERE with-E
– muru
2 days ago
The escaped+in basic regular expressions is a non-standard GNU extension.
– Kusalananda
2 days ago
add a comment |
up vote
0
down vote
+ in grep need to be escaped to take effect. Instead of
echo abc123 | grep -o [a-z][0-9]+$
You need to write
echo abc123 | grep -o '[a-z][0-9]+$'
There are other characters that need to be escaped as well. It is also good practice to put your regex in single quotes.
You can also use egrep which is a synonym of grep -E and uses Extended RE, as commented by @muru.
answered 2 days ago
Weijun Zhou
1,468224
Or use ERE with-E
– muru
2 days ago
The escaped+in basic regular expressions is a non-standard GNU extension.
– Kusalananda
2 days ago
add a comment |
up vote
0
down vote
up vote
0
down vote
+ in grep need to be escaped to take effect. Instead of
echo abc123 | grep -o [a-z][0-9]+$
You need to write
echo abc123 | grep -o '[a-z][0-9]+$'
There are other characters that need to be escaped as well. It is also good practice to put your regex in single quotes.
You can also use egrep which is a synonym of grep -E and uses Extended RE, as commented by @muru.
answered 2 days ago
Weijun Zhou
1,468224
+ in grep need to be escaped to take effect. Instead of
echo abc123 | grep -o [a-z][0-9]+$
You need to write
echo abc123 | grep -o '[a-z][0-9]+$'
There are other characters that need to be escaped as well. It is also good practice to put your regex in single quotes.
You can also use egrep which is a synonym of grep -E and uses Extended RE, as commented by @muru.
answered 2 days ago
Weijun Zhou
1,468224
edited 2 days ago
answered 2 days ago
Weijun Zhou
1,468224
answered 2 days ago
Weijun Zhou
1,468224
answered 2 days ago
Weijun Zhou
1,468224
1,468224
Or use ERE with-E
– muru
2 days ago
The escaped+in basic regular expressions is a non-standard GNU extension.
– Kusalananda
2 days ago
add a comment |
Or use ERE with-E
– muru
2 days ago
The escaped+in basic regular expressions is a non-standard GNU extension.
– Kusalananda
2 days ago
Or use ERE with
-E– muru
2 days ago
Or use ERE with
-E– muru
2 days ago
The escaped
+ in basic regular expressions is a non-standard GNU extension.– Kusalananda
2 days ago
The escaped
+ in basic regular expressions is a non-standard GNU extension.– Kusalananda
2 days ago
add a comment |
IsaraSu is a new contributor. Be nice, and check out our Code of Conduct.
IsaraSu is a new contributor. Be nice, and check out our Code of Conduct.
IsaraSu is a new contributor. Be nice, and check out our Code of Conduct.
IsaraSu is a new contributor. Be nice, and check out our Code of Conduct.
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